Megacities already account for a major part of global energy-related CO2 emissions with a strong tendency to increase; hence, future climate policy has to put a special emphasis on reducing big cities' energy consumption, especially in a world, where global climate negotiations are deadlocked. Tokyo, the world's biggest metropolis and emitter of greenhouse gases roughly comparable to Scandinavian countries, started the world's first megacity carbon market in 2010, the design of which is unique, due to its focus on end-energy use in buildings. While the program only started in 2010, the first results are now available. Hence, the paper answers the question to what extend Tokyo's new carbon market can be considered a worthwhile model for other cities as well as an additional building-stone in a bottom-up global climate policy regime. By applying up-to-date sustainability economics reasoning, the paper evaluates the design and the recent results of Tokyo's carbon market, showing that, while there is still room for improvements, Tokyo has the potential to be a world leader in sustainable local climate policy.